The present invention relates to imaging systems such as cameras. In particular, the present invention is directed to a camera configured to reduce or eliminate certain types of distortion.
Imaging systems such as video cameras employing CCD""s and other photosensitive devices are used in a large number of different applications. Such uses are often carried out in environments exhibiting extreme conditions so that a great deal of reliance must rest upon the traditional optical systems that are included as part of almost all video cameras. In many cases, the operation of an electronic imaging device is not feasible without the full benefits of an accompanying, high resolution optical system. Because of advances in optical technology, the optical system per se can usually be provided without creating distortion within the focal range of the optical system. Unfortunately, electronic imaging systems often operate beyond the normal focal range of the optical systems included therein.
Traditional optical systems have curved focal regions while most electronic photosensitive devices, such as CCD""s, are manufactured on planar wafers. Traditional photosensitive chemical film is also arranged as a flat plane when taking either still or moving pictures. Thus, the interface between the optical system and the electronic photosensitive portion of a camera is far from perfect. This imperfect interface results in various types of distortion such as that caused by Petzval field curvature and positive or pincushion distortion that makes images appear fatter than they really are. Such effects also include lenticular aberrations, coma and astigmatism.
This distortion, when added to other sources of distortion, such as camera movement or changes in the optical system, due to the use of a wide angled lens, or extreme light variation, create difficulties in achieving clear, accurate images from any type of imaging system. This is further exacerbated if the video camera is being moved during it""s use, or is otherwise subject to impact during it""s use. These conditions are also problematical for traditional photosensitive chemical film cameras, but to a lesser extent.
The various types of distortion produced by electronic video cameras, especially those having electronic photosensor arrays, have been addressed in a number of ways as disclosed in a number of U.S. patents discussed below, each of which is incorporated herein by reference.
One approach is found in U.S. Pat. No. 5,489,940 to Richardson et al., which discloses a wide-angle lens producing a distorted wide-angle optical image. The electronic imaging sensor is constituted-by a plurality of imaging elements. These have a distribution on the surface of the sensor that is best described by a non-linear function. This distribution of the imaging elements corrects for the distortion in the wide-angle image. FIG. 10 of this patent depicts the arrangement of imaging sensors in the non-linear corrective pattern. However, this pattern does not fully match the optical characteristics of the lens system to the electronic sensor array in order to fully utilize the wide-angle lens, or to fully eliminate all distortion that occurs due to the discrepancy between the essentially flat electronic-image sensor and the curved focal area of the wide angle lens.
U.S. Pat. No. 5,497,191 to Yoo et al. discloses an image shake compensation circuit including a motion information detector for detecting motion information based on the occurrence of image shake when this occurs in an encoded video signal. The compensation circuit also includes a shake compensator for obtaining a start display position of the image of a present frame according to the motion information detected by the motion information detector. Also included is a decoder for decoding the encoded video signal to correct the display position of the image of the present frame in response to an output signal from the shake compensator.
U.S. Pat. No. 5,528,296 to Gove et al. discloses a graphics data unit for a digital television receiver. The graphics data unit uses a special light modulator, and has a graphics processor which offloads graphics processing tasks, such as that used for closed captioning and on-screen display. The graphics data unit also has a character memory unit, which stores fonts for closed-caption and on-screen display characters. A staggered pixel arrangement is used to compensate for distortion normally caused by standard pixel layouts for the spatial light modulator.
U.S. Pat. No. 5,552,828 to Perregaux discloses a scanner in which a set of photosensitive silicon chips are arranged together to form a single page-width array of photosensors. The photo sites along the critical ends of each chip are specially shaped to ensure even spacing of all photo-sites along the array, taking into account flaws in the dimensions of individual chips. The special shape of the end photo-site is trapezoidal or a variation of a trapezoid.
U.S. Pat. No. 3,833,762 to Gudmundsen discloses a solid state image motion compensation imager. This system uses a separate image speed sensor to control a motor which adjusts the position of the overall imaging sensor.
U.S. Pat. No. 5,179,428 to Lee discloses a three dimensional CCD image sensor including a plurality of N-type light-receiving regions formed on a two dimensional plane and a plurality of N type VCCD regions on a second two dimensional plane formed under the first plurality of regions.
U.S. Pat. No. 4,5745311 to Resnikoff et al. discloses a plurality of random array sensing devices. The sensor elements have their centers distributed on the surface of the substrate in a random, non-periodic pattern. The transfer members are coupled to the sensor elements and generate the output signal.
U.S. Pat. No. 5,460,341 to Katsuyama et al. discloses a disturbance compensation system for a camera that is mounted on a spacecraft. The system has an imaging device and condensing means for condensing light onto the imaging device. Linear actuators adjust the position of the imaging device by moving it in all directions appropriate. A control circuit computes, in response to position information associated with the imaging device, an amount by which the position of the imaging device should be corrected. The actuators that control movement of the imaging device are operated on the basis of the computed amount.
U.S. Pat. No. 5,218,442 to Hamada et al. discloses a camera with a shake detection apparatus. The camera operates so that light emitted by a subject which is passed through a photographic optical system is formed as an image on an area sensor. The system also includes an electronic view finder that indicates the image of the subject based on the output from the area sensor. An apparatus that detects image shaking caused by shaking of the camera is operated based on the output from the area sensor.
No combination of the teachings of the conventional art has suggested a technique for addressing the distortion caused by the interface between optical systems having curved focal areas and electronic photosensitive devices formed as flat planes. Consequently images derived from electronic cameras will always display a certain amount of distortion, especially at the periphery of the image captured by the imaging system.
Consequently it is an object of the present invention to increase resolution in video imaging and camera systems.
It is another object of the present invention to remove distortion caused by lenticular aberration, such as pin cushion distortion, coma and astigmatism, as well as any other effects of a Petzval field.
It is a further object of the present invention to optimize the reception and imaging of particular wavelengths of light in a video imaging system having an optical system.
It is a still another object of the present invention to reconcile discrepancies between circular optical lenses and rectangular display screens, thereby eliminating the peripheral effects found in conventional imaging systems.
These objects of the present invention, as well as the goals and advantages of the present invention, are achieved by an imaging device having an optical system with a posterior focal area. The imaging device also includes a photosensor configured to conform to and substantially occupy the posterior focal area of the optical system.
In another aspect of the present invention, the aforementioned goals are achieved by a method of compensating for distortion in an imaging system having an optical lens system and a photosensor. The method includes the steps of inputting a plurality of light rays to an area of the optical system. Then the light rays are refracted and transmitted to a plurality of photosensor devices located at a plurality of posterior focal points corresponding to the area of the optical system receiving the input light rays.